WASHINGTON – Supreme Court precedents that have stood the test of time for generations are in danger of falling like dominoes in the next few months.

First on the chopping block is a 1977 ruling that allowed public employee unions to collect fees from non-members for collective bargaining. The court's conservative justices have been itching to overrule that unanimous decision for decades.

Next up is a 1992 case in which the court refused to require that mail-order retailers collect sales taxes from buyers in other states. For years, that has given online retailers a competitive advantage over brick-and-mortar stores.

The court also will consider second-guessing one of its least-popular chestnuts — a 20-year-old ruling, based on one from 1945, that gives federal agencies broad discretion to interpret their own regulations.

Since Chief Justice John Roberts took the center seat on the court in 2005, the justices have been reticent to second-guess the decisions of their predecessors. They have done so at a pace just above once a year, considerably less often than in the past.

“That’s not an accident," says Jonathan Adler, director of the Center for Business Law & Regulation at Case Western Reserve University School of Law. "The chief justice, in particular, doesn’t like the court to be a disruptive force. He prefers to maintain stability and predictability where possible.”

It's not always possible. Roberts could not prevent the court's conservatives from overturning two of their precedents in 2010's Citizens United v. Federal Election Commission ruling, which eliminated limits on independent political spending by corporations.

And five years later, the court's decision in favor of same-sex marriage overruled a 1972 decision that found no federal basis to block states from prohibiting the practice.

The court usually adheres to the principle of stare decisis, or adhering to its earlier decisions. But occasionally those earlier rulings cry out for change and the court waits too long to correct them. Perhaps the top example is Plessy v. Ferguson, which upheld separate public facilities on the basis of race and stood for 60 years before being overruled by Brown v. Board of Education.

The court in recent years has had scores of opportunities to overrule earlier decisions and has taken a pass, according to the Supreme Court Database, a research facility housed at Washington University School of Law. The Roberts Court has done so less than any of its predecessors dating to the 1950s.

Few rulings have been up for grabs as often as Auer v. Robbins, the 1997 decision that upheld federal agencies' right to interpret their own regulations without court interference.

When the court last refused to hear a case that would have toppled Auer, dissenting Justice Clarence Thomas warned that "the doctrine is on its last gasp." Now the justices have another chance to extinguish it in a case they will consider at next week's private conference.

"You wrote it."

Thomas is fond of recounting a conversation on the bench with the late justice Antonin Scalia, who complained that "Auer is one of the worst opinions in the history of this country."

"Nino," Thomas responded, "you wrote it."

This month the court will hear a challenge to the fees paid by non-members to public employee labor unions that would overrule Abood v. Detroit Board of Education, a 1977 decision. The justices stopped short of that extreme step in 2012, 2014 and 2016.

Many of the court's conservative justices believe Abood was wrongly decided to begin with because it forces workers to contribute to a group they may disagree with. Opponents argue that as a constitutional case based on First Amendment rights, it is less sacred than rulings based on statutes that Congress can amend.

"Although this court reconsiders its precedents with caution, stare decisis does not warrant preserving Abood’s error," Solicitor General Noel Francisco argues in the government's court papers.

But Abood has its defenders, including Michael Kimberly, co-director of the Yale Law School Supreme Court Clinic.

If it's scuttled, Kimberly warns, "contracts entered into based on unions’ ability to provide specified services, funded through agency fees, would have to be renegotiated. And government employees’ existing reliance on unions’ abilities to negotiate effectively and to provide contractually required services would be eliminated."

Precedents don't last forever

The high court's consideration in April of a case that would level the playing field between online and brick-and-mortar retailers when it comes to collecting sales taxes presents a clear case of technological change influencing legal rulings.

The justices ruled 8-1 in Quill v. North Dakota in 1992 that companies selling wares by catalog across state lines were exempt from collecting sales taxes. Now that North Dakota case is being challenged by one from South Dakota.

"As this court has long recognized, stare decisis is not an inexorable command," former Solicitor General Donald Verrilli wrote in a brief for the Retail Litigation Center. "When the world changes, it is appropriate to consider whether the law should change as well."